Abstract: To address the technical challenge of insufficient roof contact in downward drift backfilling at Datun Tin Mine, this study systematically investigates the influence of paste rheological properties on flow performance through slump tests and rheological tests of full-tailings paste. The experimental results indicate that both slump and expansion degree of the paste exhibit significant negative correlations with yield stress and viscosity, with notable interaction effects between these parameters. A polynomial regression model was developed to predict rheological parameters, achieving high fitting accuracy. Random forest feature importance analysis reveals that yield stress has a greater impact on flow performance than viscosity, although both factors remain essential. The study proposes that high-flow, self-leveling performance is a critical prerequisite for achieving effective roof contact. By referencing the classification standards for high-flow self-compacting concrete, quantitative criteria for paste workability were established: spread ≥ 660 mm, slump ≥ 260 mm, corresponding to rheological parameter thresholds of yield stress ≤ 74.86 Pa and viscosity ≤ 1.07 Pa·s. Numerical simulations and industrial trials on optimized paste mixtures confirm that the improved paste exhibits significantly enhanced fluidity and increased roof contact rate. These findings provide reliable technical parameters and practical guidance for similar mine backfill engineering applications.